Numerically controlled oscillator and method of operation

Abstract

In one embodiment, the present invention is directed to a numerically controlled oscillator. The numerically controlled oscillator comprises: a phase accumulator for receiving an input digital word; and a phase to amplitude converter that is operatively coupled to the phase accumulator to receive a first phase signal and a second phase signal, the phase to amplitude converter calculating a sine value and a cosine value of each of the first and second phase signals, the phase to amplitude converter generating a summation of (i) a product of the sine value of the first phase signal and the cosine value of the second phase signal and (ii) a product of the sine value of the second phase signal and the cosine value of the first phase signal.

Description

FIELD OF THE INVENTION [0001] The present invention is related to a numerically controlled oscillator. DESCRIPTION OF RELATED ART [0002] A numerically (or digitally) controlled oscillator is an electronic system for synthesizing a range of frequencies in response to a digital signal. The range of frequencies generated by a numerically controlled oscillator is related to the bit resolution of the input digital signal and the clock used to control the numerically controlled oscillator. In particular, the generated frequencies are less than half of the frequency of the clock used to control the numerically controlled oscillator as a result of Nyquist's theorem. [0003]FIG. 1 depicts numerically controlled oscillator 100 that is controlled by N-bit frequency word 102 (Freq(k)). Specifically, frequency word 102 defines the desired operating frequency of numerically controlled oscillator 100. Frequency word 102 is applied to phase accumulator 101 that is controlled by a clock to define the...

AI Technical Summary

Benefits of technology

[0006] Representative embodiments are directed to numerically controlled oscillators and methods of operation. Representative embodiments enable a reduction in the total amount of memory used by ROM units of numerically controlled oscillators by utilizing a trigonometric identity. In one representative embodiment, a phase-to-amplitude converter receives a digital phase signal (represented by Φ) from a phase accumulator. The received digital phase signal may be a truncation or may include all of the bits from the phase accumulator. The phase-to-amplitude converter includes a first set of ROM units for storing sine and cosine values corresponding to the most significant bits (represented by θc) of Φ. The phase-to-amplitude converter includes a second set of ROM units for storing sine and cosine values corresponding to the lesser significant bits (represented by θf) of Φ. The sine and cosine values retrieved by the ROM units are combined according to sin(θc)·cos(θf)+sin(θf)·cos(θc) to generate a digital amplitude signal. Furthermore, the use of the trigonometric identity to reduce the amount of memory associated with the ROM units does not compromise the accuracy of the phase to amplitude conversion. Specifically, the use of the trigonometric identity does not involve any algorithmic error.

Problems solved by technology

If a relatively high degree of accuracy is desired, the use of a ROM structure to perform the phase to amplitude conversion requires an appreciably large amount of memory.

Although all of these mechanisms mitigate the error associated with the truncation, a degree of error remains in digital amplitude signal 105.

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